Its all about court awareness. Purvis got beat off the dribble 30 feet from the hoop which made Nolan commit and Calhoun leave his man in the corner who shot the 3.
Why is Purvis playing that aggressive 30 feet from the hoop?
Calhoun constantly makes this mistake. He tries to pressure his player out to the 3 point line rather than recognize his limitations. Unless your RB you don't have the lateral quickness (yes you too RP) to be doing that 30 feet from the hoop.
The court awareness for all our players on defense was just plain horrible for most of the year. Brimah is notoriously bad at this.